(1) Field of the Invention
The present invention relates to optical recording and reproducing methods for an optical disk having a disk surface portion in which prepits, indicative of preformat information, are formed.
(2) Description of the Related Art
Recordable optical storage media are known. Generally, in a recordable optical disk, preformat information, including address information, rotation control sync marks and record position control sync marks, is recorded. For example, a CD-R (compact disk recordable) or a MD (mini-disk) includes a disk surface portion in which wobble grooves are formed in order to derive a wobble signal, indicative of the rotation control sync information, from the wobble grooves.
As disclosed in Japanese Laid-Open Patent Application No. 9-326138, there is known an optical disk having a disk surface portion in which prepits, indicative of the preformat information (for example, the address information), are formed. In the optical disk disclosed in the above publication, the wobble grooves are formed as the tracks, and the lands between neighboring grooves are used to form the prepits at given distances along the track. These prepits are called the land prepits (LPP). Even when the track pitch is small, the prepits can be continuously formed on the lands of the disk without interruption, and the preformat information derived from such prepits of the optical disk is useful for obtaining accurate address information and accurate rotation control sync information.
FIG. 10 shows a track structure of an optical disk as disclosed in the above publication.
As shown in FIG. 10, in the disk surface portion of the optical disk, wobble grooves G are formed to extend in a tangential track direction TT of the disk, and land prepits LPP are formed on the lands L between neighboring grooves. In the optical disk in the above preformat structure, data is written in the grooves and the lands acting as a guard band. It is intended to prevent the influence of the prepits (on the lands) to the data recorded in the grooves. The lowering of recording density of the optical disk due to the preformat information can be avoided, and the compatibility with read-only optical storage media, such as CD (compact disk) and DVD (digital video disk), can be maintained.
As disclosed in the above publication or Japanese Laid-Open Patent Application No. 9-17029, a method of detecting the preformat information from the optical disk of the above type is known.
In the preformat information detection method of the above publications, a push-pull signal is derived from a reflected laser beam from the optical disk by using a 4-segment photodetector. The push-pull signal is supplied to a high-pass filter, and the direct-current component of the push-pull signal is eliminated by the high-pass filter. The resulting signal is converted into a digital signal by using a slicer (comparator). The digital signal is subjected to demodulation so that a prepit signal indicative of the preformat information, such as the address information, is produced.
In a conventional optical recording method, an optimal recording power is predetermined which is the most suitable laser power of a laser light source for minimizing the amount of jitter in data recording. In the conventional optical recording method, this optimal recording power is used to record data to the optical disk, with respect to the entire track of the optical disk, even when the optical disk of the type shown in FIG. 10 is accessed.
FIG. 12A through FIG. 12E are diagrams for explaining a conventional optical recording method. FIG. 12A shows a waveform of a push-pull signal produced at an output of a high-pass filter. FIG. 12B shows a waveform of a prepit signal derived from the push-pull signal. FIG. 12C shows a waveform of a data signal produced by an EFM (eight-to-fourteen modulation) decoder. FIG. 12D shows a waveform of an LD (laser diode) emission power signal. FIG. 12E shows a pattern of write marks recorded along a track of the optical disk in accordance with the LD emission power signal.
When recording write marks along a track (groove) of the optical disk at the optimal recording power, the LD emission power waveform of FIG. 12D is used. As shown in FIG. 12E, the groove xe2x80x9cGxe2x80x9d is interposed between the neighboring lands xe2x80x9cLxe2x80x9d, and this prevents the write marks from radially extending beyond the boundaries between the groove G and the lands L. Hence, the write marks xe2x80x9cMxe2x80x9d have a radial width which is substantially equal to a radial width of the groove xe2x80x9cGxe2x80x9d.
However, in the optical disk of the type of FIG. 10, the prepits xe2x80x9cLPPxe2x80x9d are formed on the lands L before data is recorded to the optical disk. As shown in FIG. 12E, the center write mark xe2x80x9cMxe2x80x9d which is located radially adjacent to the prepit xe2x80x9cLPPxe2x80x9d may extend beyond the boundary between the groove G and the land L (with the prepit LPP). This causes the reflected laser beam from the prepit LPP of the optical disk to be lowered due to the presence of the write mark M adjacent to the prepit LPP. Also, the amplitude of the push-pull signal corresponding to this position of the optical disk will be lowered. The amplitude of a prepit signal in the conventional optical recording method may be significantly degraded due to the presence of the write mark radially adjacent to the corresponding prepit in the optical disk.
FIG. 11A shows a prepit signal before recording, and FIG. 11B shows a prepit signal after recording which may be produced in the conventional optical recording method.
When recording the write marks along the track (groove) of the optical disk in accordance with the data signal as shown in FIG. 12C, the write marks and the spaces between write marks on the groove are likely to confront the positions of the prepits on the neighboring lands with equal probability. The amplitude of the prepit signal always varies in accordance with the prepit pattern.
As shown in FIG. 11A, the amplitude of the prepit signal before the write marks are recorded to the optical disk is highly stable without significant degradation. By comparing the prepit signal with a slice level of the slicer, it is possible to accurately detect the preformat information from the optical disk.
However, if the write marks are already recorded along the entire track of the optical disk at the optimal recording power, the amplitude of the prepit signal becomes significantly unstable as shown in FIG. 11B. For example, when the prepit on the land aligns with the write mark on the neighboring groove, the peak amplitude of the prepit signal is reduced to below xc2xd of the peak amplitude of FIG. 11A. In such a case, the prepit signal cannot be properly detected by using the slice level of the slicer. When the prepit on the land aligns with the space between write marks on the neighboring groove, the peak amplitude of the prepit signal is substantially the same as the peak amplitude of FIG. 11A. For this reason, it is difficult for the conventional optical recording method to provide accurate detection of the preformat information from the optical disk.
Further, as disclosed in Japanese Laid-Open Patent Application No. 5-128564, a method of detecting the wobble signal from the optical disk of the above type is known. The conventional optical reproducing method of the above publication is aimed at obtaining accurate detection of the wobble signal even when a tilt of the optical axis of the objective lens with respect to the optical disk surface arises. In the method of the above publication, the gains of outputs from two photodiodes of a 2-segment photodetector are adjusted to be equal to each other. A difference signal indicative of a difference between the reproducing signals output from the photodiodes is produced by subtraction, and the difference signal is passed through a wobble decoder so that the rotation control sync information is produced the wobble signal. However, when the write mark is radially adjacent to the prepit in the optical disk, it is difficult for the conventional optical reproducing method to accurately detect the wobble signal and the prepit signal from the optical disk with data written thereto.
As disclosed in Japanese Laid-Open Patent Application No. 6-290462, a method of detecting the wobble signal from the optical disk of the above type is known. The conventional optical reproducing method of the above publication is aimed at obtaining accurate detection of the wobble signal. In the method of the above publication, the outputs from two photodiodes of a 2-segment photodetector are supplied to two normalization circuits, and a sum signal indicative of a sum of the outputs of the photodiodes is supplied to the normalization circuits. The reproducing signals output from the photodiodes are normalized at the normalization circuits by the sum signal. A difference signal indicating of a difference between the normalized signals is produced by subtraction, and the difference signal is passed through a band-pass filter so that the wobble signal is produced. However, when the write mark is radially adjacent to the prepit in the optical disk, it is difficult for the conventional optical reproducing method to accurately detect the wobble signal and the prepit signal from the optical disk with data written thereto.
An object of the present invention is to provide improved optical recording and reproducing methods in which the above-described problems are eliminated.
Another object of the present invention is to provide an optical recording method which allows accurate detection of the preformat information from the optical disk with data written thereto, by minimizing the degradation of the prepit signal when the write mark is radially adjacent to the prepit in the optical disk.
Another object of the present invention is to provide an optical reproducing method which provides accurate detection of the wobble signal and the prepit signal from the optical disk with data written thereto, with good reliability, even when the write mark is radially adjacent to the prepit in the optical disk.
Another object of the present invention is to provide a wobble/prepit detection method for optical recording and reproduction of the optical disk, which provides accurate detection of the wobble signal and the prepit signal from the optical disk with data written thereto, with good reliability, even when the write mark is radially adjacent to the prepit in the optical disk.
The above-mentioned objects of the present invention are achieved by an optical recording method for an optical disk having a disk surface portion in which prepits, indicative of preformat information, are formed, the optical recording method including the steps of: detecting a portion of a data signal which matches one of the prepits and corresponds to a write mark radially adjacent to one of the prepits; recording marks along a track of the disk, using an optimal recording power, in accordance with a non-match portion of the data signal which does not match any of the prepits but corresponds to a write mark, the recorded marks having a first width in a radial direction of the disk; and recording marks along the track of the disk, using a proper recording power level, in accordance with the match portion of the data signal, the recorded marks having a second width in the radial direction which is smaller than the first width.
The above-mentioned objects of the present invention are achieved by an optical reproducing method for an optical disk having a disk surface portion in which wobble grooves indicative of rotation control sync information are formed to create a wobble signal, and prepits indicative of preformat information are formed to create a prepit signal, the optical reproducing method including the steps of: providing an automatic gain control AGC unit for each of photodiodes contained in a photodetector of a pickup, the AGC units being connected to the photodiodes, and each AGC unit providing a gain of a detection current output by a corresponding one of the photodiodes; detecting a portion of a data signal which matches one of the prepits and corresponds to a write mark radially adjacent to one of the prepits; detecting the wobble signal and the prepit signal along a track of the disk, using optimal gains of the AGC units, in accordance with a non-match portion of the data signal which does not match any of the prepits but corresponds to a write mark; and detecting the wobble signal and the prepit signal along the track of the disk, using reduced gains of half of the AGC units and the optimal gains of the other half of the AGC units, in accordance with the match portion of the data signal.
The above-mentioned objects of the present invention are achieved by a wobble/prepit detection method for optical recording and reproduction of an optical disk having a disk surface portion in which wobble grooves indicative of rotation control sync information are formed, and prepits indicative of preformat information are formed, the wobble/prepit detection method including the steps of: detecting a portion of a data signal which matches one of the prepits and corresponds to one of write marks radially adjacent to one of the prepits; detecting a wobble signal and a prepit signal along a track of the disk, using an optimal track offset, in accordance with a non-match portion of the data signal which does not match any of the prepits but corresponds to one of the write marks; and detecting the wobble signal and the prepit signal along the track of the disk, using a corrected track offset, in accordance with the match portion of the data signal, the corrected track offset having a margin of a prepit detection error to a permissible level, which margin being larger than a margin corresponding to the optimal track offset.
In a preferred embodiment of the optical recording method of the invention, the write marks are recorded along the track of the disk by selectively using one of the optimal recording power or the proper recording power level in accordance with the non-match portion or the match portion of the data signal. The radial width of the marks recorded in accordance with the match portion of the data signal is smaller than the radial width of the marks recorded in accordance with the non-match portion of the data signal. The optical recording method of the present invention is effective in minimizing the degradation of the prepit signal due to the presence of the write mark radially adjacent to the prepit in the optical disk, allowing accurate detection of the preformat information, such as the address information of the optical disk.
In a preferred embodiment of the optical reproducing method of the invention, the wobble signal and the prepit signal are detected along the track of the optical disk by selectively using the optimal gains or the reduced gains of the AGC units in accordance with the non-match portion or the match portion of the data signal. Even when the write mark is radially adjacent to the prepit in the optical disk, it is possible to accurately detect the wobble signal and the prepit signal from the optical disk with good reliability.
In a preferred embodiment of the wobble/prepit detection method of the invention, the wobble signal and the prepit signal are detected along the track of the optical disk by selectively using the optimal track offset or the corrected track offset in accordance with the non-match portion or the match portion of the data signal. Even when the write mark is radially adjacent to the prepit in the optical disk, it is possible to accurately detect the wobble signal and the prepit signal from the optical disk with good reliability.